Myeloproliferative disorders (MPD) are conditions where too many blood cells are produced. MPDs include: Childhood Acute Myeloid Leukemia and Other myeloid malignancies such as childhood myelodysplastic syndromes; Acute Myeloid Leukemia (AML); Chronic Myelogenous Leukemia (CML); Chronic Myeloproliferative Disorders such as Polycythemia Vera, Chronic Idiopathic Myelofibrosis, Essential Thrombocythemia, Chronic Neutrophilic Leukemia, and Chronic Eosinophilic Leukemia; Myelodysplastic Syndromes such as refractory anemia, refractory anemia with excess blasts, refractory anemia with ringed sideroblasts, refractory cytopenia with multilineage dysplasia, unclassifiable myelodysplastic syndrome, myelodysplastic syndrome associated with del (5q), de novo Myelodysplastic Syndrome, secondary Myelodysplastic Syndrome and “previously treated” Myelodysplastic Syndrome; and Myelodysplastic/Myeloproliferative Neoplasms such as Chronic Myelomonocytic Leukemia, Juvenile Myelomonocytic Leukemia (JMML), Atypical Chronic Myeloid Leukemia (aCML) and Myelodysplastic/Myeloproliferative Neoplasm, unclassifiable.
Chronic Myelogenous Leukemia (CML), also known as chronic myeloid leukemia or chronic granulocytic leukemia (CGL), is a malignancy of a hematopoietic stem cells characterized by a cytogenetic abnormality, the Philadelphia chromosome in 95% of the patients (Druker, 2008; Faderl et al., 1999a; Faderl et al., 1999b). It accounts for 15-20% of all cases of adult leukemia.
CML is a progressive, uniformly fatal disease in untreated patients. It is often divided into three phases: a chronic phase lasting three to six years; an acute or accelerated phase lasting three to six months; and a final blast crisis phase. The progression of the disease to blast crisis results in rapid death due to infections, bleeding and leukemic organ infiltration.
The Philadelphia chromosome or Philadelphia translocation is a specific cytogenetic abnormality that is the hallmark of CML, but can also be found in other myeloproliferative disorders, including ALL and AML. It results from a reciprocal chromosomal translocation between chromosome 9 and 22: t(9; 22)(q34; q11). The translocation produces a fusion gene, termed BCR-ABL (Ren, 2005), created by the translocation of the c-ABL proto-oncogene form its normal position on chromosome 9 chromosome 22. The region on chromosome 22 was named breakpoint cluster region (BCR) and spans 5.3 kilobases. ABL is a non-receptor tyrosine kinase that is expressed in most tissues and BCR is a signaling protein. The BCR-ABL fusion has constitutively activated tyrosine-kinase activity, which is essential for the transforming activity and leukemogenicity. Depending on the chromosomal break point different forms of BCR-ABL protein with different molecular weights, p185 BCR-ABL (p185 BCR-ABL is also known as p190 BCR-ABL), p210 BCR-ABL and p230 BCR-ABL, are generated.
Ph+ leukemias are induced by the chimeric BCR-ABL oncogene resulting from the fusion of the BCR gene to the N-terminus of the c-ABL gene. The BCR gene, on chromosome 22, breaks either at exon 1, exon 12/13, or exon 19 and fuses to the c-ABL gene on chromosome 9 to form, respectively, three types of BCR-ABL chimeric gene: P190 (also known as P185), P210, or P230. The three forms of BCR-ABL contain the same portion of the c-ABL gene but different lengths of the BCR gene. BCR comprises three domains: a coiled-coil structure, serine-rich sequences, and the C-terminal domain. P190 contains the first two domains of BCR, and P210 and P230 also contain some and the majority of the C-terminal domain of BCR, respectively. The C-terminal domain that is lacking in the P190 BCR protein comprises Pleckstrin homology (PH) and dbl-like domains (present in both P210 and P230). P230 contains in addition the calcium-phosphate biding (CalB) domain and the first third of the domain associated with GTPase activating activity for p21rac (GAPrac) of the BCR region.
In humans, each of the three forms of the BCR-ABL oncogene is associated with a distinct type of leukemia. The P190 form is most often present in B-ALL but only rarely in CML (Deininger M W et al., Blood (2000) 96:3343-56). P210 predominates in CML and in some acute lymphoid (Deininger et al. supra) and myeloid leukemias in CML blast crisis. P230 was found in a very mild form of CML and in a few patients with typical CML (Pane F et al., Blood (1996) 88:2410-2414; Wilson et al., Blood (1997) 89:3064; Mittre et al., Blood (1997) 89:4239; Briz et al., Blood (1997) 90:5024). Lymphoid blast crisis of CML and Ph+ B-ALL account for 20 percent of adults and 5 percent of children with acute B-lymphoid leukemia that is caused by BCR-ABL and other oncogenes. Among those patients with BCR-ABL-induced B-ALL, 50 percent of adults and 20 percent of children carry P210 form of BCR-ABL and the rest of the patients carry the P190 form (Deininger et al. supra; Sawyers C L N. Engl. J. Med. (1999) 340:1330-1340; Druker B J et al., N. Engl. J. Med. (2001) 344:1038-1042). Thus, both P190 and P210 can induce Ph+ B-ALL, and only P210 is a major inducer of CML.
Transition from chronic phase to blast crisis is a devastating process in Ph+ leukemia. While in most patients, chronic phase CML can be temporarily controlled with cytotoxic drugs such as imatinib, the disease can progress from chronic phase to accelerated phase or blast crisis within several years of diagnosis. Although the mechanism underlying the disease progression remains unclear, additional genetic alterations seem to play a role in this process. Mutations in the BCR-ABL fusion gene, of tumor suppressor genes, including the retinoblastoma gene (Rb), p16, and p53, have been found to be associated with CML blast crisis patients (Towatari M et al., Blood (1991) 78:2178-2181; Sill H et al., Blood (1995) 85:2013-2016; Feinstein E et al., Proc. Natl. Acad. Sci. U.S.A. (1991) 88:6293-6297). Several studies have shown that BCR-ABL deregulates the functions of DNA repair-related genes. For example, BCR-ABL down-regulates expression of the DNA repair enzyme DNA-PKcs (Deutsch E et al., Blood (2001) 97:2084-90). P210BCR-ABL may interact with the Xeroderma pigmentosum group B protein, which could lead to the impairment of DNA repair function (Takeda N et al., Proc. Natl. Acad. Sci. USA (1999) 96:203-207). Expression of two other genes related to genetic stability, BRCA-1 and RAD51, is also deregulated by BCR-ABL (Canitrot Y et al., Oncogene (1999) 18:2676-2680; Slupianek A et al., Mol Cell (2001) 8:795-806). BCR-ABL can also cause over-expression and increased activity of the error-prone polymerase β, leading to an increased mutagenesis (Canitrot et al. supra).
The field of stem cell biology has stimulated cancer biologists to identify and characterize cancer stem cells in tumors. Such cancer stem cells are rare but are critical for the formation and growth of tumors (Jordan et al., 2006; Pardal et al., 2003; Reya et al., 2001; Rossi et al., 2008; Singh et al., 2003; Wang and Dick, 2005), and are thought to be required for the initiation of tumors (Al-Hajj et al., 2003).
For leukemia such cancer stem cells are called leukemic or leukemia stem cells (LSCs). The concept of LSCs was first described in the 1970s (Park, C. H. et al., J. Natl. Cancer Inst., 46: 411-422), although the existence of LSC was demonstrated only more recently (Blair, A., et al., 1997, Blood 89:3104-3112 and Bonnet, D. et al., 1997 Nature Med., 3: 730-737). It is currently thought that a few LSCs are sufficient to induce leukemia, accumulate mutations and can give rise to abnormal new hematopoietic tissues. LSCs similar to normal hematopoietic stem cells do not proliferate at a high rate.
The responsiveness of patients to current treatments, particularly treatment with kinase inhibitors, is often transient since patients develop resistance to these drugs.
Thus, while some treatments have been developed to address myeloproliferative disorders, there is a continuing need for therapeutic methods and compositions to treat myeloproliferative disorders. In particular, new treatments are required in view of resistance to current treatments in patients. In particular, there is a continuing need for therapeutic methods and compositions to treat CML.